1. Field of the Invention
The present invention relates to a technology for controlling a call based on a signal transmitted from a terminal in a mobile communication network.
2. Description of the Related Art
In recent years, the 3rd Generation Partnership Project (3GPP), which is a group for standardizing the third generation mobile communication systems, has been working on the standardization of the IP Multimedia Subsystem (IMS). The IMS is a specification for communication to change the services that have been so far used in the fixed networks and the mobile communication and the broadcast systems into Internet Protocol-based (IP-based) services so that integrated multimedia services can be offered (See “3GPP TS 23. 228V7. 2. 0, searched on Dec. 26, 2005 on the Internet <URL: http://www.3gpp.org/ftp/Specs/html-info/23228.htm>).
FIG. 6 is a block diagram of a typical mobile communication network defined by the IMS. The mobile communication network includes n (where n is a positive integer) terminals 101 to 10n, such as mobile phones, and n application servers 201 to 2n. Subscribers to the network service (hereinafter, “subscribers”) use the terminals 101 to 10n to enjoy various kinds of multimedia services including telephone call services that are offered by the communication carrier through the application servers 201 to 20n. When the subscribers use those services, sessions are established via the three types of Session Initiation Protocol (SIP) servers, namely Proxy Call Session Control Functions (P-CSCFs) 401 to 40n, an Interrogating Call Session Control Function (I-CSCF) 50, and Serving Call Session Control Functions (S-CSCFs) 601 to 60n. The mobile communication network further includes a Home Subscriber Server (HSS) 30 that is a server that manages subscriber information, authentication information, billing information, and the like. In the subscriber information managed in the HSS 30, for each of the subscribers, information about an S-CSCF that serves as a storing destination for the subscriber is specified.
The SIP is used as a protocol for controlling the communication among the terminals 101 to 10n, the P-CSCFs 401 to 40n, the I-CSCF 50, and the S-CSCFs 601 to 60n. The SIP is one of the communication control protocols that are used for internet phones and the like. With the SIP, sessions are generated, changed, and discontinued among the terminals. The DIAMETER is used as a protocol for controlling the communication among the I-CSCF 50, the S-CSCFs 601, to 60n, and the HSS 30. The DIAMETER is one of the authentication protocols that are used for performing a user authentication process in a remote access.
The P-CSCFs 401 to 40n are SIP servers, and the terminals 101 to 10n make access first to one of the P-CSCFs 401 to 40n. The P-CSCF 401 to 40n forward SIP messages received from the terminals 101 to 10n to the I-CSCF 50 or one of the S-CSCFs 601 to 60n. When a P-CSCF from among the P-CSCFs 401 to 40n receives an SIP message from a terminal from among the terminals 101 to 10n for registering the current position of the terminal (hereinafter, a “registration request message”), that P-CSCF forwards the registration request message to the I-CSCF 50.
The I-CSCF 50 is an SIP server that receive a registration request transmitted from a terminal of a subscriber and making connections to home networks (the networks that are owned by communication carriers, and each home network corresponds to one communication carrier or one type of service) and other networks. Although only one I-CSCF, i.e., the I-CSCF 50, is shown in FIG. 6, generally, one I-CSCF 50 is provided for every home network. When the I-CSCF 50 receives a registration request message from any of the P-CSCFs 401 to 40n, the I-CSCF 50 selects one of the S-CSCFs, based on storing S-CSCF information, which is defined for each of the subscribers and is included in the subscriber information managed in the HSS 30, and forwards the registration request message to the selected S-CSCF. If no storing S-CSCF information exists in the HSS 30, the I-CSCF 50 selects one of the S-CSCFs on its own, using a predetermined method.
The S-CSCFs 601 to 60n are SIP servers that perform user authentication processes and manage sessions, for example. The S-CSCFs 601 to 60n offer various kinds of multimedia services in collaboration with the application servers 201 to 20n based on the subscriber information managed in the HSS 30. When a S-CSCF from among the S-CSCFs 601 to 60n receives a registration request message from the I-CSCF 50, that S-CSCF performs a user authentication process for the subscriber who has transmitted the registration request message, and subsequently generates a session.
To summarize, when a terminal transmits a registration request message, a P-CSCF forwards the message to a I-CSCF. Further, the I-CSCF forwards the message to a S-CSCFs based on subscriber information managed in a HSS. Then, the S-CSCF performs a user authentication process for the subscriber based on the registration request message and also establishes a session.
Thus, in the conventional IMS network, the signals transmitted from the terminals are concentrated in the I-CSCF, which is provided only one for every home network. Thus, depending on the number of the signals, a huge amount of load can be put on the I-CSCF and cause some sort of problems. Therefore, there is a need of a technology that can reduce the load on the I-CSCF.